Purification of glycerin



l-fl 7 COMPOUNDS,

Aug. 7, 1945. A H. E. HoYT 2,381,055-

PURIFICATION OF GLYCERIN Filed lay 18, 1943 Patented Aug. 7, 1945 UNITED STATES PATENT GFFICE 2,381,055 PURIFICATION F GLYCEBIN Howard E. Hoyt, Stamford, Conn., aasignor to dustrial Chemi U. S.In

cals, Inc., New York,

N. Y., a corporation of Delaware Application May 18, 1943, Serial No. 487,444

Claims. (Cl. 26o-637) This invention relates to the purification of glycerin and particularly to the recovery of glycerin free from acid, saponlflable matter and other impurities from crude glycerin obtained by fermentation and particularly from a residue commonly known as distillery slop.

The recovery ofglycerin from fermentationoperations has been the subject of much investigation, but thesolution of the problem is diiilcult owing tothe presence of large quantities of extraneous material from which the glycerin must be separated. An eifective method of separating a water solution of glycerin from distillery slop is described in the application of Wolcott Dennis Serial No. 408,837, filed August 29, 1941. According to the method described in that application, the distillery slop is sprayed into a stream of inert gas at an elevated temperature. The solids formed by evaporation are separated and the glycerin solution is condensed from the va-- pors. The aqueous glycerin solution contains ordinarily about 25% or more by weight of glycerin. In addition to water, the solution contains some free'acid, considerable saponiable matter (esters or combined acids) and other impurities. Repeated experiments have demonstrated that the usual procedure of heating the glycerin solution with a soluble alkali such as sodium'hydroxide followed by distillation of the alkaline so-I lution does not prevent the occurrence oi' free acid in the distilled glycerin.

It is the object of the invention to provide a practical and commercially applicable method of purifying crude glycerin solutions containing free acids and saponinable matter whereby the undesirable contaminating materials are substantially eliminated and pure glycerin of a satisfactory commercial quality is obtained.

Other objects and advantages of the invention will be apparent as it is better understood by ref'- erence to the following speciiication and the accompanying drawing, showing a now sheet which Pharmacopoeia XI. Following the treatment with sulphuric acid, I add sufficient lime to neutralize all free acids and to provide an excess for the purpose of saponifying the combined*- acids. After saponincation, the solution is acidifled with sulphuric, acid to precipitate the lime as calcium sulphate which is removed by filtration. At this point any acid present will be in the form of free-acid. This is removed by treating the solution with an acid-adsorbing synthetic resin. Finally, thel solution is distilled to recover glycerin free from acid and saponlilable matter.

Theprocedurewillbereadilyunderstoodby reference to the drawing",in which l and l lndicate the sources of supply of crude glycerin and sulphuric acid which are added Y properproportions and subjected. to luotndigestionL as. indicated at 1. Steam may be introduced at 8;' and the volatile acids resulting from the ,digestionT are removed at l. The introduction ofV steam is. however, optional. I prefer to employ commercial concentrated sulphuric acid. From 5% to 15% by weight of the glycerin present is usuallyrequired. 10% by weight of the glycerin present normally ensures a satisfactory reaction, and the effective separation of the impurities which can be removed at this stage of the process. A temperature of C. is satisfactory in this operation. although considerable variation ispomble.

Following the initial step, the solution is delivered to the saponiiier I Il and lime,..us'ually in` the form of lime paste prepared with water, is introduced from a source Il inquantity sumcient to neutralize the acid and to afford sufiicient excess to saponify the combined acids which may be present. The amount required will l vary, of course, and may be readily after determination of the amount of acid and vsaponiilable matter which is present in the solution. I'he mixture'is maintained at an appropriate temperaturefor example about' 110 .C. The temperature is not critical.'` Air is intro- -duced at I2 and volatile bases resulting from saponiiication are withdrawn at I3.

When saponiilcation has been completed, the mixture is cooled and at i4 is subjected to acidication with sulphuric acid from a source. Il. It

is preferable-to acidity until the solution has a pH of approximately 3. After thorough mixing,`

to ensure complete reaction, the mixture is illtered at I6. the precipitated salts, principally calcium sulphate. being separated as the lter cake at I1.' l

The nitrate is then subjected to an anion-ad- VUUI VII ll IUUI! 2oU.UHuv|1slHY,l;AnsuN COMPOUNDS.

MOSS Hotel cuco sorbent resin at Il. Several such esins are known. They are in general the product of condensation of organic amines or similar basic materials with formaldehyde. One known as Anex is believed to be a melamine resin since it conpresent and to sapOnifycombined acids. adding tains about 33% nitrogen. Another, "Amberli sulphuric acid to the solution of such neutraliza- ]:R, 4" is the product. of condensation 0f organic tion and saponiileation treatment to precipitate amines such as aniline with formaldehyde. The alkaline-earth metal present as the sulphate. Sepinvention is not limited to the use oi.' these pareretins the precipitated sulphate. subiectins the ticular products, as any resin having anion-adi0 x'elnail'lln Solution t0 an anion adcibing resin sorption activity can be used to accomplish the ll0 eliminate acid present therein, and nally diS- purpose, The treni-,nient may consist of passing tilling the solution to recover glycerin free fro the solution through a suitable column or other acid and Saponillable matter receptacle containing pieces of the resin of a size 2# The method of purifying a glycerin Solution adaptedi'to ensure substantial surface contact.V l5 containing ncl" less than about 60% by weight when the resin has been depleted, it may be seoi' glycerin obtained from fermentation residues vivlned readily by mst washing it and then passand. ccntinins free acids and sepcninble meting an aqueous Vsolution or sodium carbonate 'lei' which comprises digesting auch glycerin Sollitm-ough the column, After rinsing with water' tion with sulphuric acid at a. temperature suillthe resin with its activity renewed may be emciitilily hitill catise the iiligi'iiic icidriig i'eci" myth' c w con au presen e g yce so ugseisfor the er treatment of gly erin so tion, mixing the resulting solution with a sufll- The solution, many freed from acid by the cientcamount of an alkaline-earth metal comaction of the aniomadsorbent resin, is distilled pound to neutralize free acid present and to saat I9, and the pure glycerin is separated at 20. poiiiiy combined acids adding siiipliiii'ic acid io As an example of the invention, 12.9 kilograms the solution ofv such neutralization and saponiof a crude glycerin Soluon obtained the cation treatment to precipita alkaline-earth method of theDennis application Ser.No.408,837 metal pi'eeelit a8 the Sulphate Separating che contained by analysis about 3.01 kilograms of precipitated Sulphate Slibieciing the remaining together free acid and Saponinable Solution to an anion adsorbing resin to eliminate matter equivalent respectively to 64.2 cc. and acid Present therein' and man? disiimng the 228.0 cc. or normal alkali per 100 grams of glyc- Solution ilo lecoiei' glycerin ii'ee from acid and erin. This was ilrst concentrated until enough siipoiiiiiaiiie mattei'- water hadbeen removed to leave a solution con- 3" The method of piii'iiYii-ig il' concentrated' taining about by weight of glycerin. The so- 35 glycerin solution obtained from fermentation lution was iirst treated with 10 parts by weight of concentrated sulphuric acid for every 100 parts by weight of glycerin and heated to 140 C. while a current of steam was passed through the solution. Thereafter the solution was mixed with 384 grams of'lime in the form of a paste with water, and the mixture was heated to about 110 C. while a stream of air was passed through the solution. The mixture was then cooled and sul` phuric acid was added until the solution indicated a pH of 3. The precipitate was then removed by iiltration. 'I'he illtrate was passed through a bed consisting of small pieces of Anex equivalent to 1.2 liters in volume. The free acids present were adsorbed by the resin, and the emuent 5H glycerin contained neither free nor combined and iinally discllling the Solution t0 reccver glycacids. Upon distillation ofthe filtrate after erin free from acid and SaPOnlable metter. treatment with "unex," 2.32 kilograms er e pred- 4- The method cf purifying ai concentrated uct having a glycerin content of 97.9% by weight glycerin solutionv obtained from fermentation were obtained. Thelover-all recovery of glycerin 55 residues and containing free acids and Saponiin the mein fraction. needs, roots and sweetwailable matter. which comprises digesting such ter, was approximately 91% of the amount conconcentrated glycerin .50111111011 With Sulphuric tained in the starting msteriaL acid in amount equal to about 5% to 15% of the The procedure as dessi-med affords s, simple weight of the glycerin of the solution and at a and eiective method of recovering glycerin of 0o temperature Sufllcienlly high t0 cause the sulcommercial quality from crude raw material. plilll'ic acid licl'eacli with contaminante Present The apparatus req d vis of the type normauy in the glycerin solution, mixing the resulting sofound in plants ada d for chemical treatment lullion Wiilii a Slmcieiii amount of an alkaline' of materials and consequently it is not described earth metal Compound t0 neutralize free acid indsi-,siL present and to saponify combined acids, adding Various changes may be made in the demis of sulphuric acid to the solution of such neutralizathe procedure without departing from the invention and saponiflcation treatment to precipitate tion or sacriilcing the advantages thereof. alkaline-'earth I netel present as the sulphate. Iclaim: separating the precipitated sulphate. subiecting 1. The method of purifying -a concentrated the remaining Scluticnto an anion adsorblng glycerin solution obtained from fermentation resin to eliminate acid present therein, and ilnalresidues and containing free acids and snponm- 1y distillins the solution to recover glycerin free able matter, which comprises digesting such conc-1 frgmagdpgiillfeygttncommted u1 huric aci e cenmted glycerin solution with s p Glycerin solution obtained from fermentation at a temperature suillciently high to cause the sulphuric acid to react with con ts present in the glycerin solution. mixing the resulting solution with a suillcient amount of an alkaf line-earth metal compound to neutralize free acid residues and containing free acids and saponiliable matter. which comprises digesting such concentrated glycerin solution with sulphuric acid at a temperature of about C. whereby 4o the sulphuric acid is caused to react with contaminants present in the glycerin solution, mixlng the resulting solution with a suillcient amount of an alkaline-earth metal compound to neutralize free acid present and to saponify combined acids. adding sulphuric acid to the solution of such neutralization and saponiilcation treatment to precipitate alkaline-earth metal present as .the sulphate, separating the precipitated sulphate,

subjecting the remaining solution to an anion adsorbing resin to eliminate acid present therein,

sulphui-ic acid to the solution of such neutraliza- 10 tion and saponication treatment until the acidity thereof is brought to a pH of about; 3 to precipitate alkaline-earth metal present as the sulphate, separating the precipitated sulphate, subjecting the remaining solution to an anion adsorbing resin to eliminate acid present therein, and finally distillingthe solution to recover glycerin free from acid and saponiable matter.

HOWARD E. HoYT. 

